It was an unforgettable day for me. I joined the demonstrators in Cairo, along with the hundreds of thousands across Egypt who went on to the streets on Tuesday demanding freedom and bravely facing off the fearsome violence of the police. The regime has a million and a half soldiers in its security apparatus, upon which its spends millions in order to train them for one task: to keep the Egyptian people down.

I found myself in the midst of thousands of young Egyptians, whose only point of similarity was their dazzling bravery and their determination to do one thing – change the regime. Most of them are university students who find themselves with no hope for the future. They are unable to find work, and hence unable to marry. And they are motivated by an untameable anger and a profound sense of injustice.

I will always be in awe of these revolutionaries. Everything they have said shows a sharp political awareness and a death-defying desire for freedom. They asked me to say a few words. Even though I've spoken hundreds of times in public, this time it was different: I was speaking to 30,000 demonstrators who were in no mood to hear of compromise and who kept interrupting with shouts of "Down with Hosni Mubarak", and "The people say, out with the regime".

I said I was proud of what they had achieved, and that they had brought about the end of the period of repression, adding that even if we get beaten up or arrested we have proved we are not afraid and are stronger than they are. They have the fiercest tools of repression in the world at their disposal, but we have something stronger: our courage and our belief in freedom. The crowd responded by shouting en masse: "We'll finish what we've begun!"

I was in the company of a friend, a Spanish journalist who spent many years in eastern Europe and lived through the liberation movements there. He said: "It has been my experience that when so many people come out on to the streets, and with such determination, regime change is just a matter of time."

So why have Egyptians risen up? The answer lies in the nature of the regime. A tyrannical regime might deprive the people of their freedom, but in return they are offered an easy life. A democratic regime might fail to beat poverty, but the people enjoy freedom and dignity. The Egyptian regime has deprived the people of everything, including freedom and dignity, and has failed to supply them with their daily needs. The hundreds of thousands of demonstrators are no more than representatives of the millions of Egyptians whose rights have been invalidated.

While public calls for reform in Egypt long predated the dissent in Tunisia, events there were of course inspiring. Now people could clearly see the security apparatus could not protect the dictator for ever. And we had greater cause than our Tunisian counterparts, with more people living in poverty, and under a ruler who has held the reins of power even longer. At some point, fear made Ben Ali flee Tunisia. We could emulate the success of that protest; some people on Cairo's streets copied the same French slogan, "Dégage, Mubarak". And by today, uprisings had also reached Arab states such as Yemen.

Already the authorities are finding their tactics cannot stop the protests. Demonstrations have been organised through Facebook as a reliable, independent source of information; when the state tried to block it, the people proved more clever, and bloggers passed on ways to bypass the controls. And the violence of the security services is a risk for both sides: in Suez people have risen up against police who shot demonstrators. History shows that at some point ordinary policemen will refuse to carry out orders to kill fellow citizens.

More ordinary citizens are now defying the police. A young demonstrator told me that, when running from the police on Tuesday, he entered a building and rang an apartment bell at random. It was 4am. A 60-year-old man opened the door, fear obvious on his face. The demonstrator asked the man to hide him from the police. The man asked to see his identity card and invited him in, waking one of his three daughters to prepare some food for the young man. They ate and drank tea together and chatted like lifelong friends.

In the morning, when the danger of arrest had receded, the man accompanied the young protester into the street, stopped a taxi for him and offered him some money. The young man refused and thanked them. As they embraced the older man said: "It is I who should be thanking you for defending me, my daughters and all Egyptians."

That is how the Egyptian spring began. Tomorrow, we will see a real battle.